The present invention relates to a brazeable aluminum alloy sheet and a process of making same. More particularly, the present invention relates a brazeable aluminum alloy sheet for making fins for heat exchangers such as condensers, evaporators, radiators and coolers particularly for automobiles.
It is known in the art that the fins of heat exchangers are made of Al-Mn alloy sheets or brazing sheets having cores of the Al-Mn alloy sheets coated with a Al-Si brazing agent on both sides or on one side. The fins and the tubular elements are brazed to each other.
Recently there have been strong demands for lightweight vehicles and the reduced production cost. To meet these demands thin sheets are made but the thin sheets are likely to deform, that is, to bend under load and to buckle when they are subjected to brazing heat. It is therefore essential that the thin sheets must have an anti-deflection ability without trading off the formability. In order to be anti-deflectable, their heat resistance must be increased, and also it is required that the crystals in the sheet texture grow fully owing to recrystallization at the brazing heat. The growth of crystals increases the heat resistance of the sheets. If the crystals are small, the grain boundaries increase which introduces a molten brazing agent into the depth of the sheet texture, thereby allowing it to erode the sheet texture from inside. As a result, the sheets lose their strength. In contrast, the large crystals reduce crystal boundaries, thereby preventing the molten brazing agent from eroding the sheet texture.
It has been found through the long period of use that the Al-Mn alloy sheet lacks sufficient anti-deformation ability.
To improve this drawback one prior art example teaches that one or two of Si, Sn, Zn, Mg, and Zr are added to the Al-Mn alloy (for example, Japanese Patent Kokai (unexamined) No. 63-125635). Another example teaches that one or two of the high melting point metals in the Va and VIa families such as Ta, Nb, Mo and W are added thereto (Japanese Patent Kokai (unexamined) No. 63-125636). A further example teaches that the final working in the cooling period after annealing is controlled to improve the production process (Japanese Patent Kokai No. 63-125635). However, there has been no successful expedient which satisfies the strong demand for thin fins.
In order to increase the corrosion resistance of tubular elements for heat exchangers, In or Zn is added to make the fins sacrificial anodes. However, the addition of In and Zn decreases the anti-deflection ability of the sheets.